The present invention pertains to a device for checking the adjustment of a light source in an incident light microscope having a revolving lens turret. The device comprises a centering cylinder which has an observation orifice and is shaped essentially like a lens, so that it can be inserted into the revolving lens turret and thus can be brought into the path of the illuminating beam.
In incident light microscopy there are often difficulties encountered with regard to the accurate adjustment of the source of light, in that the object to be viewed is not illuminated to a uniform brightness. In order to determine whether the light source is adjusted correctly or whether its position must be corrected, a device of the afore-mentioned type is known which has a deflecting element in the optical axis, for example, a planar mirror inclined by 45.degree. to the optical axis. By means of this mirror, the image of the light source is reproduced on a ground glass plate arranged parallel to the optical axis. The illuminating beam reflected by the mirror passes through a window provided in the housing of the device, so that the image of the light source (coiled filament or light spot) may be viewed and focused sharply by adjustment of the collecting lens in the lamp housing. Mounting a deflecting element inside the device and providing an observation window in its housing is expensive from a manufacturing standpoint. In the course of screwing this known centering device into the revolving lens turret, imaging inaccuracies may occur if the window therein is to face the observer.